Spreading code sequence acquisition system and method that allows fast acquisition in code division multiple access (CDMA) systems

ABSTRACT

Methods for generating code sequences that have rapid acquisition properties and apparatus which implement the methods by processing spreading codes on in-phase and quadrature channels. A first method combines two or more short codes to produce a long code. This method may use many types of code sequences, one or more of which are rapid acquisition sequences of length L that have average acquisition phase searches r=log2L. Two or more separate code sequences are transmitted over the complex channels. If the sequences have different phases, an acquisition may be done by acquisition circuits in parallel over the different code sequences when the relative phase shift between the two or more code channels is known. When the received length L codes or the length L correlation codes used to find the phase of the received codes have a mutual phase delay of L/2, the average number of tests to find the code phase of the received code is L/4. The codes sent on each channel may be the same code, with the code phase in one channel being delayed with respect to the other channel, or they may be different code sequences.

This application claims the benefit of U.S. Provisional Application60/000,775 filed Jun. 30, 1995.

BACKGROUND OF THE INVENTION

The present invention generally pertains to Code Division MultipleAccess (CDMA) communications, also known as spread-spectrumcommunications. More particularly, the present invention pertains to anew system and method employing a new code sequence design for providingfast acquisition of a received spreading code phase in a CDMAcommunications system.

DESCRIPTION OF THE RELEVANT ART

Recent advances in wireless communications have used spread spectrummodulation techniques to provide simultaneous communication by multipleusers. Spread spectrum modulation refers to modulating a informationsignal with a spreading code signal; the spreading code signal beinggenerated by a code generator where the period Tc of the spreading codeis substantially less than the period of the information data bit orsymbol signal. The code may modulate the carrier frequency upon whichthe information has been sent, called frequency-hopped spreading, or maydirectly modulate the signal by multiplying the spreading code with theinformation data signal, called direct-sequence (DS) spreading.Spread-spectrum modulation produces a signal with bandwidthsubstantially greater than that required to transmit the informationsignal. The original information is recovered at the receiver bysynchronously demodulating and despreading the signal. The synchronousdemodulator uses a reference signal to synchronize the despreadingcircuits to the input spread-spectrum modulated signal in order torecover the carrier and information signals. The reference signal may bea spreading code which is not modulated by an information signal. Suchuse of a synchronous spread-spectrum modulation and demodulation forwireless communication is described in U.S. Pat. No. 5,228,056 entitledSYNCHRONOUS SPREAD-SPECTRUM COMMUNICATIONS SYSTEM AND METHOD by DonaldL. Schilling, which techniques are incorporated herein by reference.

One area in which spread-spectrum techniques are used is in the field ofmobile cellular communications to provide personal communicationservices (PCS). Such systems desirably support large numbers of users,control Doppler shift and fade, and provide high speed digital datasignals with low bit error rates. These systems employ a family oforthogonal or quasi-orthogonal spreading codes, with a pilot spreadingcode sequence synchronized to the family of codes. Each user is assignedone of the spreading codes as a spreading function. Related problems ofsuch a system include: handling multipath fading effects. Solutions tosuch problems include diversity combining of multipath signals. Suchproblems associated with spread spectrum communications, and methods toincrease capacity of a multiple access, spread-spectrum system aredescribed in U.S. Pat. No. 4.901,307 entitled SPREAD SPECTRUM MULTIPLEACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS byGilhousen et al. which is incorporated herein by reference.

The problems associated with the prior art systems focus around reliablereception and synchronization of the receiver despreading circuits tothe received signal. The presence of multipath fading introduces aparticular problem with spread spectrum receivers in that a receivermust somehow track the multipath components to maintain code-phase lockof the receiver's despreading means with the input signal. Prior artreceivers generally track only one or two of the multipath signals, butthis method may not be satisfactory because the combined group of lowpower multipath signal components may actually contain far more powerthan the one or two strongest multipath components. The prior artreceivers track and combine the strongest components to maintain apredetermined Bit Error Rate (BER) of the receiver. Such a receiver isdescribed, for example, in U.S. Pat. No. 5,109,390 entitled DIVERSITYRECEIVER IN A CDMA CELLULAR TELEPHONE SYSTEM by Gilhousen et al. Areceiver that combines all multipath components, however, is able tomaintain the desired BER with a signal power that is lower than that ofprior art systems because more signal power is available to thereceiver. Consequently, there is a need for a spread spectrumcommunication system employing a receiver that tracks substantially allof the multipath signal components, so that substantially all multipathsignals may be combined in the receiver, and hence reduce the requiredtransmit power of the signal for a given BER.

Providing quality telecommunication services to user groups which areclassified as remote. Such as rural telephone systems and telephonesystems in underdeveloped countries, has proved to be a challenge inrecent years. These needs have been partially satisfied by wirelessradio services, such as fixed or mobile frequency division multiplex(FDM), frequency division multiple access (FDMA), time divisionmultiplex (TDM), time division multiple access (TDMA) systems,combination frequency and time division systems (FD/TDMA), and otherland mobile radio systems. Usually, these remote services are faced withmore potential users than can be supported simultaneously by theirfrequency or spectral bandwidth capacity.

The problems associated with the prior art systems focus around reliablereception and synchronization of the receiver despreading circuits tothe received signal. Since spreading code sequences in a communicationssystem which supports a relatively large number of users may be verylong with a corresponding long code period, one particular problemassociated with prior spread spectrum receivers is to rapidly determinethe correct code phase of a received spread spectrum signal. Onesolution of fast acquisition of the correct spreading code phase is toform spreading code sequences with specific characteristics which areceiver can derive from a particular received code phase.

For example, prior art systems employ a method in which a code generatorproduces a pseudorandom code of length N, divides the code in half togenerate two new codes with code period N/2, and multiplies the datawith each code for transmission over an In-phase and Quadrature channel.The receiver only searches for the occurrence of the short code periodon the I or Q channel. The advantage of the system is that the number ofusers supportable with codes of length N can be transmitted with abandwidth necessary to support codes of length N/2. Such a system isdescribed in U.S. Pat. No. 5,442,662 entitled CODE-DIVISIONMULTIPLE-ACCESS COMMUNICATIONS SYSTEM PROVIDING ENHANCED CAPACITY WITHINLIMITED BANDWIDTH to Fakasawa et al. with is incorporated herein byreference.

Another method and apparatus for producing a composite code for fastacquisition in a CDMA system may employ a code that is made to appearmore complex by the use of one or more masking codes. The composite codegenerator comprises a plurality of component code generators. Thecomposite codes are used to modulate in-phase and quadrature channels. Areceiver has enhanced speed of acquisition because of the shorter timeneeded to search for composite codes in the quadrature channel, and theplurality of component codes of the in-phase channel are derived fromthe codes used in the quadrature channel. Such a system is described inU.S. Pat. No. 5,022,049 entitled MULTIPLE ACCESS CODE ACQUISITION SYSTEMto Abrahamson et al. which is incorporated herein by reference.

In related CDMA systems, a two-tier ciphering method ensures security bycycling code masks. A pseudorandomly generated code key is used toselect one of a plurality of scrambling masks. A variant of this methoduses orthogonal code hopping or random code hopping. A CDMA system canbe viewed as encoding an information signal into blocks of L codesymbols, and each block is then encoded with a scrambling mask of lengthL. A system of this type is described in U.S. Pat. No. 5,353,352,entitled CALLING CHANNEL IN CDMA COMMUNICATIONS SYSTEM to Dent et al.which is incorporated herein by reference.

SUMMARY OF THE INVENTION

Rapid acquisition of the correct code phase by a spread-spectrumreceiver is improved by designing spreading codes which are faster todetect. The present embodiment of the invention includes a new method ofgenerating code sequences that have rapid acquisition properties byusing one or more of the following methods. First, a long code may beconstructed from two or more short codes. The new implementation usesmany code sequences, one or more of which are rapid acquisitionsequences of length L that have average acquisition phase searchesr=log2L. Sequences with such properties are well known to thosepracticed in the art. The average number of acquisition test phases ofthe resulting long sequence is a multiple of r=log2L rather than half ofthe number of phases of the long sequence.

Second, a method of transmitting complex valued spreading code sequences(In-phase (I) and Quadrature (Q) sequences) in a pilot spreading codesignal may be used rather than transmitting real valued sequences. Twoor more separate code sequences may be transmitted over the complexchannels. If the sequences have different phases, an acquisition may bedone by acquisition circuits in parallel over the different codesequences when the relative phase shift between the two or more codechannels is known. For example, one of two sequences may he sent on anIn phase (I) channel while the other is sent on the Quadrature (Q)channel. To search the code sequences, the acquisition detection meanssearches the two channels, but begins the (Q) channel with an offsetequal to one-half of the length of the spreading code sequence. With acode sequence length of N, the acquisition means starts the search atN/2 on the (Q) channel. The average number of tests to find acquisitionis N/2 for a single code search, but searching the (I) and phase delayed(Q) channel in parallel reduces the average number of tests to N/4. Thecodes sent on each channel may be the same code, with the code phase inone channel being delayed with respect to the other channel, or they maybe different code sequences.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a typical code division multiple accesscommunication system spreading code acquisition detector of the priorart.

FIG. 2 is a block diagram of the spreading code acquisition detector ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

In a CDMA communication system where they are a number of users, eachuser's signal is coded using a unique code sequence. Consequently, areceiver can detect the signal coming from a particular user. The firststep in establishing a communication link with a user is to acquire thereceived spreading code phase. Typically, this process includesdetermining the phase (shift) of the observed sequence.

Communication is not possible until the proper spreading code phase hasbeen determined. The invention described here in a new method ofdesigning the code sequences such that a receiver can rapidly determinethe received code sequence phase.

Generally, in a spread spectrum communication system, the receiver doesnot initially know the received spreading code phase. A particularsystem may “guess” at a spreading code phase and attempt to despread thereceived signal. If the despread signal is despread, the receiverdeclares synchronization, but if the signal is not despread, thereceiver adjusts the locally generated code phase to a new value(“guess”) and repeats the test. An exemplary acquisition system is shownin FIG. 1.

Referring to FIG. 1, the received signal r(t) is applied to a multiplier101 and multiplied by the locally generated code sequence signal c(t) toattempt to despread the received signal r(t). The signal produced afterthe despreading either corresponds the received signal power plus noisepower is the locally generated code phase is synchorinzed to thereceived spreading code phase, or corresponds to noise power only if thelocally generated code phase is not synchronized to the receivedspreading code phase. Since the despread signal is a narrowband signalcompared to the bandwidth of the spreading code, the output signal ofthe despreader is applied to the filter 102, which can be a bandpass ormatched filter. The output despread signal is applied to the energydetector 103, which is used to measure the despread signal power.

The decision logic 104 compares the despread signal power to apredetermined threshold value V_(τ) to decide whether the locallygenerated code phase is synchronized to the received signal. Thedecision logic provides a decision value to the control logic whichdetermines whether synchronization is achieved. If there issynchronization, the search is stopped, but if synchronization has notbeen achieved, the control logic (105) adjusts the code phase of thelocally generated signal c(t) by sending the appropriate code phaseadjustment signal s(t) to the spreading code waveform generator (106).

The appropriate code phase adjustment signal s(t) is determined bysearch technique implemented in the control logic (105). Existingsystems typically employ serial search techniques, which are well knownin the art. Using these techniques, each code phase is searched one at atime in sequence. Other search techniques may be used, such as aZ-search method by which each code phase before and after a chosen codephase is searched alternatively, each test increasing the phase shift ofthe tested code phase from the initial chosen code phase. This techniqueis commonly used to resynchronize a system which has temporarily lostcode phase synchronization.

the method of one embodiment of the present invention uses a transmittedspreading code sequence (a long sequence) which is generated using twoshort sequences. The long sequence (the new code sequence) is formed byrepeating one of the short sequences according to a predetermined methoddefined by the second short sequence. For example, if the first shortsequences is 0110 and the second short sequence is 1100, and if thepredetermined method is such that the first sequence is repeated as itis for each 1 in the second sequence and inverted for each 0 in thesecond sequence, the long sequence is 0110 0110 1001 1001. In anothermethod the first short sequence is repeated as it is when the bit valuein the second sequence does not change, and the first sequence isinverted when the bit value in the second sequence changes from 1 to 0or 0 to 1. In this example, the long sequence would be 0110 0110 10010110.

A specific embodiment of the applicant's invention uses maximal lengthsequences (m-sequences). The m-sequences are generated using shiftregister circuits as is well known in the art. These sequences have theimportant property that if a shift register of length r is used, theperiod of the m-sequence is N=2′−1, and so r-bit portion of them-sequence repeats in a period (each r bit section occurs only once in aperiod). The implication of this property is that, when the second shortsequence described above is an m-sequence, the acquisition circuit needsto search only r=log₂N phases of the sequence instead of N phases, whichmakes acquisition much faster.

For example, if the first short sequence has a length of 511 codeperiods or chips, and the second short sequence (m-sequence) has alength of 1023 code periods. Then the long sequence (the final sequenceis of length 511×1023=522753. Since 1023=2¹⁰−1, the acquisition circuitwill acquire the code in at most 511×10=5110 phases instead of 522753phases. Therefore the worst-case acquisition is over one hundred timesfaster.

It may be desirable for the short code phase to have boundaries whichare aligned with information symbols that are transmitted through thechannel. Because symbols are typically represented by 2^(n) bits, symbolboundaries will occur on even-numbered bit boundaries. As describedabove, the short code has a length of 511 code periods. In order for theshort code to be aligned with symbol boundaries when the symbols eachinclude 2^(n) bits, it may be desirable to concatenate another bit,either 1 or 0 onto the 551 511 length first short sequence to form a 512short code. In this instance, the length of the long sequence would be512×1023=523776 code periods. Alternatively, the second short sequencemay be extended to be an even number of code periods. For example, ifthe second short sequence were extended to 1024 bits, the length of thelong sequence would be 511×1024=523264 code periods.

To further decrease the acquisition time, one embodiment of theinvention transmits complex valued spreading code sequences (In-phase(I) and Quadrature (Q) sequences) in a pilot spreading code signal,rather than transmitting real valued sequences. Two or more separatecode sequences may be transmitted over the complex channels. If there isa known phase shift between the codes, an acquisition may be done inparallel over the different code sequences.

In this embodiment, one sequence is used to modulate the In phaseIn-phase (I) carrier while the other phase modulates the Quadrature (Q)carrier. To search the code sequences, the acquisition detection meanssearches the two channels simultaneously. If there is no phase shiftbetween the two code phases, the acquisition means begins the search onthe (I) channel at the beginning of the code sequence, but begins the(Q) channel with an offset equal to one-half of the spreading codesequence length. For this example, the acquisition means may searcheither channel beginning at any particular phase, as long as the searchof the other channel begins by offsetting the search by a predeterminedcode sub-period. For example, with a code sequence length of N, theacquisition means start the search at N/2 on the (Q) channel. Theaverage number of tests to find acquisition is N/2 for a single codesearch, but searching the (I) and phase delayed (Q) channel in parallelwith an initial offset of N/2 code periods, reduces the average numberof tests to N/4. The codes sent on each channel may be the same code,the same code sequence but delayed in one channel, or different codesequences.

An exemplary embodiment of a receiver which uses the fast acquisitionsequences of the present invention is shown in FIG. 2. The receivedsignal r(t) is demodulated by the synchronous In-phase demodulator 201and by the synchronous Quadrature modulator 202 to produce in phasein-phase channel signal r_(r)(t) and quadrature channel signal r_(Q)(t).

For the in phase in-phase channel signal r_(r)(t), the locally generatedcode sequence begins searching the received in phase in-phase channelwith the long code spreading code sequence using a predetermined initialcode phase. After despreading in multiplier 203, the in-phase signal isapplied to a bandpass, envelope or matched filter 207 to produce adespread. Next, the energy detector 209 generates a measure of thesignal power in the in-phase channels and applies this measure todecision logic 211. The decision logic 211 compares the despread signalenergy with the predetermined threshold V_(π) with three possibleoutcomes. First, the measured energy level may indicate that the codephase of the locally generated despreading code sequence from thequadrature in-phase channel spreading code generator 205 corresponds toacquisition of the correct code phase of the long code sequence. In thisinstance, the control logic 215 provides long code synchronizationsignals to spreading code generators 205 and 206 to lock the code phaseof the generator 205 and to adjust the generator 206 to the offset codephase. Second, the measured energy level may indicate that the locallygenerated code phase corresponds to acquisition of the short code phase,in which case the control logic 215 provides short code synchronizationsignals to the spreading code generators 205 and 206, and initiates thenext series of tests. These tests adjust the locally generated codesequence signal phases by the length of the short code instead of by theperiod of one code sequence value until synchronization of the long codeis found. Third, the measured energy level may indicate that the locallygenerated code phase does not correspond to synchronization of eitherthe long or short code, in which case the control logic continues theserial search by adjusting the phases of the locally generated codesequences by one code sequence period for each successive test.

The system operates in the same way for the quadrature channel signalr_(Q)(t). The locally generated code sequence has a phase which isoffset by one-half of a code period of the locally generated codesequence used to despread the in phase channel signal r_(r)(t). Afterdespreading in multiplier 204, bandpass, envelope or matched filteringin the filter 208, and measuring the despread quadrature signal power inthe energy detector 210, the decision logic 212 compares the signal to apredetermined threshold V_(rQ) to determine one of three possibilities.First, whether the code phase of the locally generated despreading codesequence from the quadrature channel spreading code generator 206corresponds to acquisition of the correct code phase of the long codesequence, in which case the control logic 215 provides the long codesynchronization signals to spreading code generators 206 and 205 to lockand adjust their respective code phases. Second, whether the locallygenerated code phase corresponds to acquisition of the short code phase.As with the in-phase channel, in this instance, the control logic 215provides short code synchorinzation signals to the spreading codegenerators 205 and 206, and performs the next series of tests byadjusting the locally generated code sequence signal phases by thelength of the short code until synchronization of the long code isfound. Third, whether the locally generated code phase doe s notcorrespond to synchronization of either the long or short code in whichcase the control logic continues the serial search by adjusting thelocally generated code sequences phases by one code sequence period foreach successive test.

Further, the control logic 215 may adjust the threshold values V_(π) andV_(rQ) to greater values when the short code is detected on either thein-phase or quadrature channels to increase the probability of detectionand decrease probability of false detection.

While the invention has been described in terms of an exemplaryembodiment, it is contemplated that it may be practiced as outlinedabove with modifications that are within the scope of the followingclaims.

The invention claimed is:
 1. A fast acquisition apparatus for quicklysynchronizing a spreading code phase of a spread-spectrum communicationsystem to a transmitted code signal having a transmitted in-phase (I)code signal and a transmitted quadrature (Q) code signal, saidtransmitted I-code signal including a first spreading code sequence andsaid transmitted Q-code signal including a second spreading codesequence; the transmitted I-code signal and the transmitted Q-codesignal having a predetermined mutual code sequence phase offset value,the fast acquisition apparatus comprising: receiving means for receivingthe transmitted code signal and for separating, from the received codesignal, the transmitted I-code signal and the transmitted Q-code signal;correlating means for correlating code sequences with the transmittedcode signal and comprising an I-code signal correlator and a Q-codesignal correlator; a local code sequence generator responsive to a codecontrol signal value to generate a local portion of the I-code sequencehaving an I-code phase value and a local portion of the Q-code sequencehaving a Q-code phase value; and controller means for determining,obtaining and maintaining code sequence lock said controller meanscoupled to the I-code signal correlator, the Q-code signal correlator,and the local code sequence generator, said I-code signal correlatorcorrelating said local portion of the I-code sequence with saidtransmitted I-code signal and generating an I-high value provided tosaid controller means when the I-code phase value of the local portionof the I-code sequence and a code phase value of the transmitted I-codesignal have matching code phase values and said Q-code signal correlatorcorrelating said local portion of the Q-code sequence with saidtransmitted Q-code signal and generating a Q-high value provided to saidcontroller means when the Q-code phase value of the local portion of theQ-code sequence and a code phase value of the transmitted Q-code signalhave matching code phase values; wherein said controller means usingsaid predetermined mutual code sequence phase offset value, generatesthe code control signal value to lock the I-code phase value of thelocal portion of the I-code sequence responsive to the I-high value andto set the Q-code phase value of the local portion of the Q-codesequence, and generates the code control signal value to lock the Q-codephase value of the local portion of the Q-code sequence responsive tothe Q-high value and to set the I-code phase value of the local portionof the I-code sequence; and said controller means is responsive to theabsence of the I-high value and the Q-high value to generate the codecontrol signal value which adjusts the I-code phase value and the Q-codephase value.
 2. The fast acquisition apparatus of claim 1, wherein thefirst spreading code sequence is equivalent to the second spreading codesequence, and the transmitted I-code signal and the transmitted Q codesignal have the predetermined mutual code sequence phase relationshipsuch that the respective code phases are not identical.
 3. The fastacquisition apparatus of claim 1, wherein the first spreading codesequence and the second spreading code sequence are each chosen from aplurality of fast acquisition sequences of length L code periods; eachof said fast acquisition sequences including a short code portion havinglength of N code periods and a long code portion having length of M codeperiods and having a mean search value of log 2L phases wherein saidshort code portion occurs repetitively, where L, M and N are integers,wherein: said local portion of the I-code sequence includes anI-sequence equivalent to the short code portion of the respective fastacquisition sequence, and said local portion of the Q-code sequenceincludes a Q-sequence equivalent to the short code portion of therespective fast acquisition sequence; said I-code signal correlatorfurther includes means for generating an I-middle value when the I-codephase value of the local portion of the I-code sequence and the codephase of the transmitted I-code signal have code phase values whichcorrespond to the I-sequence being in phase with one occurrence of therespective short code sequence of the first spreading code sequence;said Q-code signal correlator further includes means for generating aQ-middle value when the Q-code phase of the local portion of the Q-codesequence and the code phase of the transmitted Q-code signal have codephase values which correspond to the Q-sequence being in phase with oneoccurrence of the respective short code sequence of the second spreadingcode sequence; and said controller is responsive to the I-middle valueand to the absence of the I-high value and the Q-high value forgenerating the code control signal having a value which adjusts theI-code phase value and the Q-code phase value to maintain the respectivelocal short code sequence portion of the local portion of the I-codesequence in phase with each respective occurrence of the short codesequence of the first spreading code sequence; and being responsive tothe Q-middle value and the absence of the I-high value and the Q-highvalue for generating the code control signal value for adjusting theI-code phase value and the Q-code phase value to maintain the respectiveQ-sequence of the local portion of the Q-code sequence in phase witheach respective occurrence of the short code sequence of the secondspreading code sequence.
 4. The fast acquisition apparatus of claim 3,wherein N is an even integer and M is an odd integer.
 5. The fastacquisition apparatus of claim 3, wherein N is an odd integer and M isan even integer.
 6. The fast acquisition apparatus of claim 3, wherein Lis equal to M multiplied by N.
 7. The fast acquisition apparatus ofclaim 3, wherein L is equal to the least common multiple of M and N. 8.The fast acquisition apparatus of claim 3, wherein the first spreadingcode sequence and the second spreading code sequence are shifted inphase by L/2 code sequences relative to each other.
 9. A fast codeacquisition detector for a code division multiple access receiverwherein the code sequence of the signal to be received has I-code andQ-code signal components which have a known phase relationshipcomprising: an I-code despreader for despreading an I-code signalcomponent with a despreading sequence at a selected phase value andoutputting the result; a Q-code despreader for despreading a Q-codesignal component with a despreading sequence at a selected phase valueand outputting the result; and a controller for controlling the selectedphase values of said I-code and Q-code despreaders in response to aphase acquisition correlation of each of the outputs of said I-code andQ-code despreaders such that: said I-code despreader is provided aninitial I-code phase value and said Q-code despreader is provided withan initial Q-code phase value which is off-set a predetermined amountfrom said I-code initial phase value; if the correlation of the outputof neither said I-code or Q-code despreaders indicates signal phaseacquisition, said controller selectively increments the selected phasevalue of said I-code and Q-code despreaders; and if the correlation ofthe output of one of said I-code and Q-code despreaders indicates phaseacquisition, said controller selectively increments the selected phasevalue of the other despreader based on the known phase relationship sothat both despreaders output a phase correct despread signal.
 10. A fastcode acquisition detector according to claim 9 further comprising: afirst demodulator having a received signal input and a filtered I-codesignal output coupled to said I-code despreader; and a seconddemodulator having a received signal input and a filtered Q-code signaloutput coupled to said Q-code despreader.
 11. A fast code acquisitiondetector according to claim 9 wherein: said I-code despreader includes aphase adjustable spreading sequence generator which generates anI-despreading sequence at said selected phase value as controlled bysaid controller; and said Q-code despreader includes a phase adjustablespreading sequence generator which generates a Q-despreading sequence atsaid selected phase value as controlled by said controller.
 12. A fastcode acquisition detector according to claim 9 wherein: each of theI-code and Q-code signal components has a code sequence period of lengthL consisting of a plurality of subsequences having a period of length N,where L and N are integers such that L>N; and said controller controlsthe selected phase values of said I-code and Q-code despreaders inresponse to a correlation of each of the outputs of said I-code andQ-code despreaders such that said controller increments the selectedphase value of said I-code and Q-code despreaders by N is thecorrelation of either said I-code or Q-code despreaders indicates phaseacquisition of the signal N-period subsequences and the correlation ofthe output of neither said I-code or Q-code despreaders indicates signalphase acquisition.
 13. A fast code acquisition detector according toclaim 12 further comprising: a first correlator associated with saidcontroller having an I-code despreader energy output detector whichutilizes a first threshold for detection of despread N-periodsubsequences or a higher second threshold; and a second correlatorassociated with said controller having a Q-code despreader energy outputdetector which utilizes a first threshold for detection of despreadN-period subsequences or a higher second threshold; and said correlatorsusing said second higher threshold after either correlator detectsacquisition of despread N-period subsequences.
 14. A fast codeacquisition detector according to claim 9 wherein each of the I-code andQ-code signal components has a code sequence period of length L andwherein the phase relationship between the I-code and Q-code signalcomponents is a phase shift of L/2 whereby said controller selects acorrect phase value for said despreaders within L/4 iterations of phaseacquisition correlations.
 15. A fast code acquisition detector for acode division multiple access receiver, wherein the code sequence of thesignal to be received has a period of length L consisting of a pluralityof subsequences having a period of length N, where L and N are integerssuch that L>N, comprising: a despreader for despreading a signal with adespreading sequence at a selected phase value and outputting theresult; and a controller for controlling the selected phase value ofsaid despreader in response to a phase acquisition correlation of theoutput of said despreader such that: said despreader is provided aninitial phase value; if the correlation of the output of said despreaderdoes not indicate signal phase acquisition or phase acquisition of thesignal N-period subsequences, said controller increments the selectedphase value of said despreader by one; and if the correlation of theoutput of said despreader indicates phase acquisition of the signalN-period subsequences, but not signal phase acquisition, said controllerincrements the selected phase value of said despreading by N.
 16. A fastcode acquisition detector according to claim 15 further comprising: acorrelator associated with said controller having a despreader energyoutput detector which utilizes a first threshold for detection ofdespread N-period subsequences or a higher second threshold; and saidcorrelator using said second higher threshold after said correlatordetects acquisition of despread N-period subsequences.
 17. A fast codeacquisition detection method for a code division multiple accessreceiver wherein the code sequence of the signal to be received hasI-code and an Q-code signal components which have a known phaserelationship comprising: despreading an I-code signal component with adespreading sequence at a selected phase value to produce a despread Isignal; despreading a Q-code signal component with a despreadingsequence at a selected phase value to produce a despread Q signal;controlling the selected phase values of said I-code and Q-codedespreading in response to a phase acquisition correlation of thedespread I and Q signals; said I-code despreading being performed at aninitial I-code phase value and said Q-code despreading being performedat an initial Q-code phase value which is off-set a predetermined amountfrom said I-code initial phase value; if the correlation of neither thedespread I or Q signals indicates signal phase acquisition, selectivelyincrementing the selected phase value of said I-code and Q-codedespreading; and if the correlation of one of the despread I or Qsignals indicates phase acquisition, selectively incrementing theselected phase value of the other despreading based on the known phaserelationship so that both said I-code and Q-code despreading producephase correct despread signals.
 18. A fast code acquisition detectionmethod according to claim 17 further comprising: demodulating andfiltering a received signal input to produce a filtered I-code signalcomponent for said I-code despreading; and demodulating and filtering areceived signal input to produce a filtered Q-code signal component forsaid Q-code despreading.
 19. A fast code acquisition detection methodaccording to claim 17 wherein each of the I-code and Q-code signalcomponents has a code sequence period of length L consisting of aplurality of subsequences having a period of length N, where L and N areintegers such that L>N, and wherein the controlling of the selectedphase values of said I-code and Q-code despreading in response to acorrelation of said I and Q signals is such that the incrementing of theselected phase value of said I-code and Q-code despreading is by N whenthe correlation of either said I or Q signal indicates phase acquisitionof the signal N-period subsequences and the correlation of the output ofneither said I or Q signal indicates signal phase acquisition.
 20. Afast code acquisition detection method according to claim 19 furthercomprising: correlating said I signal based on energy detection at afirst threshold for detecting despread N-period subsequences or at ahigher second threshold; correlating said Q signal based on energydetection at a first threshold for detecting of despread N-periodsubsequences or at a higher second threshold; and said correlating beingat said second higher threshold after either I signal or Q signalcorrelating detects acquisition of despread N-period subsequences.
 21. Afast code acquisition detection method for a code division multipleaccess receiver, wherein the code sequence of the signal to be receivedhas a period of length L consisting of a plurality of subsequenceshaving a period of length N, where L and N are integers such that L>N,comprising: despreading a signal with a despreading sequence at aselected phase value to produce a despread signal; and controlling theselected phase value of said despreading in response to a correlation ofthe despread signal against a predetermined threshold; initiallydespreading at an initial phase value; and if the correlation of thedespread signal does not indicate signal phase acquisition or phaseacquisition of the signal N-period subsequences, incrementing theselected phase vale of said despreading by one; and if the correlationof the despread signal indicates phase acquisition of the signalN-period subsequences and the correlation does not indicate signal phaseacquisition, incrementing the selected phase value of said despreadingby N.
 22. A fast code acquisition detection method according to claim 21further comprising: correlating said despreading based on energydetection at a first threshold for detection of despread N-periodsubsequences or at a higher second threshold; and said correlating beingat said second higher threshold after the correlating detectsacquisition of despread N-period subsequences.